Fabrics used for manufacturing air bags are required in general to process a limited and controlled air permeability. As will be appreciated, such fabrics are generally woven structures formed from synthetic yarns made up of a plurality of individual filaments. Formation of such fabrics may be carried out on weaving machines using air-jet, water-jet or mechanical means for insertion of filling yarns between a plurality of warp yarns in a manner well known to those of skill in the art. Such woven textile materials are disclosed for example in U.S. Pat. No. 5,704,402 to Bowen et al.; U.S. Pat. No. 5,566,434 to Beasley; U.S. Pat. No. 5,508,073 to Krummheuer et al.; U.S. Pat. No. 5,503,197 to Bower et al.; U.S. Pat. No. 5,356,680 to Krumrheuer et al.; U.S. Pat. No. 5,421,378 to Bower et al.; U.S. Pat. No. 5,277,230 to Sollars, Jr.; U.S. Pat. No. 5,259,645 to Hirabayashi et al.; U.S. Pat. No. 5,110,666 to Menzel, et al.; U.S. Pat. No. 5,093,163 to Krummheuer et al.; U.S. Pat. No. 5,073,418 to Thornton et al.; U.S. Pat. No. 5,011,183 to Thornton et al.; U.S. Pat. No. 4,977,016 to Thornton et al.; U.S. Pat. No. 4,921,735 to Bloch and U.S. Pat. No. 3,814,141 to Iribe et al. (all specifically incorporated herein by reference).
As will be appreciated, very low controlled air permeabilities may be achieved through the use of coatings applied to the fabric construction. The primary coatings of use have been chloroprene (neoprene), silicone and other elastomeric resins. However, the use of such coatings presents a disadvantage from both an economic as well as a functional standpoint. Specifically, the use of coatings may add substantial cost while at the same time adding bulk to the finished product which translates to a greater folded volume of the final configuration thereby requiring a greater allocation of space within the vehicle deployment system.
In the attempt to avoid the use of coatings while at the same time achieving low and controlled air permeabilities, a number of approaches have been taken. The patents to Thornton et al. and Bloch propose the achievement of low permeability through the use of calendering to close the voids at the interstices between overlapping yarns in the fabric. While such calendering operations may reduce permeability, such operations also generally stiffen the fabric thereby increasing the volume requirements for a packed bag formed on such calendered material. Fabrics have also been produced using extremely tight weave constructions thereby packaging the yarns so tightly together as to achieve the desired low air permeability. One such known construction is a 420 denier nylon 6,6 fabric having 57 threads per inch in the warp and 53 threads per inch in the fill and sold under the trade designation MICROPERM® by Milliken & Company in LaGrange, Ga. A problem associated with this practice is once again the fact that the fabric produced may have relatively poor foldability due to the very high number of threads per inch within the woven construction which increases the stiffness and hence the packed volume requirement.
Packed volume (i.e. foldability) is becoming an increasingly important feature of air bag fabrics. Specifically, good foldability is crucial if the air bag is to be accommodated in the steering wheel of motor vehicles in the least amount of space. In addition, good foldability also makes possible the trouble-free inflation of the air bag for protecting a vehicle occupant in the event of a collision. Further, these issues of packing and trouble-free inflation become even more important as complex folding patterns are utilized to control initial impact in instances where an occupant may be directly facing the deploying cushion.
The difficulty in improving foldability in that processes which are recognized to generally improve the drape of a fabric and thereby its foldability such as for example, physical, pneumatic or hydraulic impingement practices also tend to dramatically increase the air permeability of the fabric to levels outside the range generally considered to be desirable. U.S. Pat. No. 5,508,073 to Krummheuer et al. (incorporated by reference), it has been proposed that improved foldability of air bag fabric can be achieved without sacrificing air permeability so long as yarns having very low filament linear densities are utilized in the construction.
In light of the above, a need exists for a fabric for use in an air bag which can be produced with improved foldability without sacrificing physical properties and without being restricted to the use of low DPF yarns. The present invention provides such a fabric and methods for producing the same and therefore represents a useful advancement over the state of the art